Adenoviruses have been extensively used as gene delivery vectors for gene therapy as well as oncolytic agents for cancer treatment. They exhibit several features that make them suitable for these applications. Namely, their structure and biology has been widely studied which allows for an easy modification of their genome, they are able to infect both replicating and non-replicating cells, and they can easily be produced at high titers for their use in the clinic. In terms of safety, they do not cause life-threatening diseases in humans, and their genome is non-integrative which prevents for insertional mutagenesis. Clinical trials with adenovirus-based vectors report a good toxicology and safety profile, although the efficacy still needs improvement, especially when the virus is administered systemically.
In the field of gene therapy, systemic administration, that is, injection into the bloodstream endovenously or intra-arterially, may be needed to reach multiple organs or disseminated cells. For example, in cancer therapy with adenovirus vectors and oncolytic adenoviruses systemic administration is necessary to treat disseminated tumours at an advanced or metastatic stage. Nonetheless, adenoviruses show important limitations when injected into the bloodstream that impair the efficacy of the therapy. Adenovirus type 5 (Ad5) suffers multiple neutralizing interactions in the bloodstream that reduce drastically the bioavailability of the virus. Liver sequestration represents the major obstacle for the therapy since >90% of the injected dose is retained by this organ, mainly by liver macrophages named Kupffer cells, but also by liver sinusoidal endothelial cells (LSECs) and hepatocytes. Direct interaction with blood cells and proteins also represents an important barrier. Ad5 can bind directly to blood cells such as erythrocytes via CAR receptor and to platelets via integrins. Antibodies not only can neutralize the virus directly but can also trigger an innate immune response by complement activation and by docking the virus particles to the Fc receptors of monocytes and neutrophils. Furthermore, vector re-administration raises the levels of anti-Ad neutralizing antibodies (NAbs) and therefore the neutralization of the virus. Adenovirus opsonization by antibodies and complement also enhances clearance by Kupffer cells. Altogether, these interactions result in a very short half-life of Ad in blood, of about few minutes in mice and humans.
Extensive efforts have been made to evade the neutralization by antibodies and immune cells when the adenovirus is systemically administered.
Chemical modification of adenovirus capsid with polymers (polyethyleneglycol (PEG) or N-(2-hydroxypropyl)methacrylamide (HPMA)) has been tested. Polymer conjugation on viral surface enabled the virus to evade neutralization by antibodies and immune cells as well as ablates CAR, integrin, and FX-binding. Nevertheless, polymers conjugated to the capsid do not pass to the virus progeny and increase the complexity of large-scale GMP production for clinical application.
WO 2011/129468 A9 discloses a chimeric adenovirus capable of evading immune recognition of neutralizing antibodies. Said adenovirus was obtained by genetic modification of the capsid of human adenovirus serotype 5, wherein the gene that codes for hexon protein was replaced by the hexon gene from simian adenovirus serotype 19. The chimeric adenovirus obtained showed also higher anti-tumour activity than the same adenovirus without the genetic modification.
Several attempts have been made in order to obtain an adenovirus shielded by albumin protein (see WO 2007/050128 A2). However, experimental evidence has demonstrated that an adenovirus having a capsid modified with an albumin-binding domain is not protected against neutralizing antibodies (Hedley S. J. et al. 2009. The Open Gene Therapy Journal, 2:1-11).
Therefore, there is still a need for further genetic modified adenovirus suitable for systemic administration and capable of escaping neutralizing antibodies.